1. Technical Field
This technology pertains generally to high temperature reactor containments, and more particularly to isolation of containments for high temperature reactors using low volatility, liquid reactor coolants.
2. Background Discussion
Fluoride-salt-cooled, high-temperature reactors (FHRs), molten salt reactors (MSRs), sodium fast reactors (SFRs), lead fast reactors (LFRs) and other liquid cooled high temperature reactors use high-temperature, low-volatility liquid coolant to transfer heat from the reactor containment structure to a process heat or power conversion heat exchanger. Because the process heat fluid or power conversion fluid (such as water, air, carbon dioxide, or helium) is normally at a higher pressure than the low-volatility liquid coolant, and may react chemically with the coolant, leaks in these process heat and power conversion heat exchangers have the potential to cause excessive pressurization, water-hammer transmission, or shock transmission into the reactor vessel and the reactor containment structure. Because the reactor vessel and containment structure provides key barriers to the release of radioactive material from the reactor during any accident, overpressure and damage to the reactor vessel and piping, as well as the containment structure, must be avoided.
The issue of mitigating overpressure has been particularly important for SFRs that use steam-Rankine power cycles, where the power conversion heat exchanger is a steam generator and very high overpressures can potentially occur if a tube leaks in the steam generator. Prior measures to prevent overpressure in SFR containment due to steam generator tube leaks include the use of double-walled steam generator tubes, the integration of a rupture disk into the steam generator, and the integration of one or more compressible gas cavities inside a steam generator.
While it is highly unlikely for a reactor vessel to leak or rupture, reactors like FHRs, SFRs and LFRs that use low-pressure liquid coolants are designed to prevent fuel from becoming uncovered and to allow continued removal of decay heat even if this occurs. Prior measures to prevent fuel from being uncovered if the reactor vessel leaks have used a “guard vessel” located outside the reactor vessel to collect the leaked coolant and limit the amount that can leak.